He would marry Ena Wertheimer.

Portrait of Ena Wertheimer: A Vele Gonfie 
1905

"I believe the 'M.' of Robert M Mathias stood for 'Moritz'."
-- Hugh Wilding

From: Tate Gallery
Report on the Painting Technique
Rica Jones
November 2001

The painting is in oil on plain-woven, linen canvas. It has a late-twentieth-century lining, the canvas a synthetic fibre and the adhesive a waxy synthetic resin. The pine stretcher is not the original; it is slightly too small for the image and has been extended to fit with a wooden batten on the left edge.

The ground is white, thin and smooth, probably a commercial priming. The paint was applied with vigourous brushwork, thin in the dark background and costume, thick in the light areas. Apart from minor drying cracks around the sitter's right hand, the paint is in very good condition. The varnish is a modern synthetic resin. A label on the back says that it was cleaned, restored and revarnished in 1976, name of firm supplied.
(Tate Gallery)

Note:
 

• See the year in review 1913
• See the Tate Gallery London